Hey Mr. Green,
Living in a 100-year-old house comes with primitive luxuries, like hand-washing the dishes. In considering a kitchen upgrade, though, I was wondering if putting in a dishwasher is a good idea. Which is greener, a dishwasher, or washing dishes by hand?
–Jocque in New Richmond, Wisconsin
As I’ve noted before, studies indicate that a dishwasher is greener than hand-washing. The EPA estimates that Energy Star-qualified dishwashers use half as much energy as hand-washing does, and 5,000 fewer gallons of water per year. To find the most efficient dishwasher brands, see the EPA’s Energy Star ratings. Some of these machines use as little as 1.6 gallons of water per cycle; many require around 3 gallons, and the maximum allowed for Energy Star is only 5.8 gallons.
However, in what may represent an epochal shift in human consciousness, more than a few men have boasted to me that their great dishwashing prowess leads them to doubt that a dishwashing machine is superior. These guys crow that their hand-washing techniques are so advanced, so ingenious, so hugely green that they can put any dishwasher to shame. Yep, they roll up their sleeves, plunge into suds up to their elbows, and simply outperform the machine. Who—among even the most optimistic reformers of domestic tasking—could have predicted that dishwashing skills might one day be upheld as a marker of manhood?
But all right, these guys may have a point. The studies I noted scrutinized a random sampling of dishwashers. It may be possible, though unlikely, given the numbers above, for the exceptional individual to get by with less water than the machine. In terms of gross water consumption, there is really only one scientific way to determine whether you're superior to the machine, and that is to wash an amount of dishes that equals the capacity of a fully loaded dishwasher, and then measure the amount of water you used.
This can be done simply by detaching the trap from your sink and allowing all the water to drain into a calibrated bucket, taking care not to let the bucket overflow. You then compare the total volume drained with the specifications of any given dishwasher. A less accurate though simpler method would be to leave the drain plugs in and carefully bail out and measure the water used rather than removing the trap. But I’m assuming that your macho dishwasher dude can handle the plumbing issue involved in trap-tampering.
Note, too, that the amount of water used doesn’t correspond exactly to the energy consumed, but will give you a rough approximation, because around 60 percent of a dishwashing machine’s total energy use is devoted to heating the water, not to running its motor.
If you do conduct such an experiment, beware the biases that can creep into the process—as they sometimes do in studies funded by various industries to prove that their products are safe and green. Use a realistic number of dishes—dishwashers can hold a lot—and don’t cheat by rinsing so superficially that you leave your dishes less clean than hygienic standards would demand.
In the interest of citizen science, I invite those who carry out this experiment to send me their results.